Dynamometer testing of vehicles is known per se, and can, for example, be carried out by roller type (rolling road) dynamometers equipped with large rollers that support the vehicle wheels, and which are used to apply a brake torque to the drive wheels of the vehicle. Such systems, however, are not always capable of providing the desired measurement accuracy and/or freedom of measurement.
Another kind of vehicle dynamometer systems for dynamometer testing of vehicles is disclosed in U.S. Pat. No. 4,669,318 (Ångström). This document relates to an apparatus for dynamometer testing of vehicles, where load absorbing means in the form of a hydrostatic pump assembly has an input shaft for engagement with a driven wheel shaft of a vehicle to be tested. Each driven wheel shaft is fixedly connected to an individual apparatus of this kind, whereby a total effective torque from the vehicle can be accurately measured.
It is also possible to perform more complex tests using a dynamometer testing system of the kind disclosed in U.S. Pat. No. 4,669,318, both for two-wheel drive systems, and also for four-wheel drive systems. Such more complex testing is, for example, disclosed in the International patent application WO2007/133154 A1 (Engstroem).
However, vehicle transmissions are becoming increasingly complex, and may include various kinds of power sources for providing power to wheel shafts of the vehicle. These power sources can be arranged to provide propelling powers, but also braking powers, e.g. when used for regenerative braking. The increased complexity of vehicle transmissions provides corresponding challenges for dynamometer testing systems. Furthermore, there is also an increasing desire to perform measurements that allows testing taking into account situations that may occur during real life driving of the vehicle on a road, such as climate related conditions that may affect the behavior of the vehicle, cold starts etc.